1. Field of the Invention
The invention relates to display systems, and more particularly, to an image processing device applied to display systems. More specifically, the invention relates to an image processing device having a pseudo-differential analog front end circuit.
2. Description of the Related Art
Many display cards (e.g., VGA card) in computer systems outputs only analog image signals in an analog format, so a liquid crystal display (LCD) is capable of displaying image frames after the analog image signal is converted into a digital image signal. Usually, the liquid crystal display utilizes an analog front end (AFE) circuit to perform signal conversion. Since the analog image signals contain three signals R, G, B, the AFE circuit includes three circuits to process the three signals respectively. A liquid crystal display controller mainly includes the AFE circuit, a scalar and a peripheral circuit. As chip integration increases, the current trend is to integrate the AFE circuit, the scalar and the peripheral circuit into a single chip (or IC).
In practical applications, three analog image signals R, G, B are usually transmitted over a cable or wire by means of single-ended signaling. In order to get rid of noise, the LCD controllers normally perform signal processing over differential signals instead of singled-ended signals, so the received singled-ended signals need to be converted into the differential signals in the interior of the LCD controllers. However, converting singled-ended signals into differential signals may cause a signal distortion problem due to different reference ground levels. The extent of signal distortion is related to the layout of the peripheral circuit and the power configuration inside the IC. If the layout of the ground plane and the power configuration have been arranged well (e.g., a four-layered board) or the IC has a lot of power pins and grounds pins (such as AD 9887), it is possible to make the signal distortion un-obvious.
Accordingly, what is needed is a circuit to address the above-identified problems. The invention addresses such a need.